The art of printing images with inkjet technology is relatively well known. In general, an image is produced by emitting ink drops from a printhead at precise moments so they impact a print medium at a desired location. The printhead is supported by a movable print carriage within a device, such as an inkjet printer, and is caused to reciprocate relative to an advancing print medium. It emits ink at times pursuant to commands of a microprocessor or other controller. The timing of the emissions corresponds to a pattern of pixels of the image being printed. Other than printers, familiar devices incorporating inkjet technology include fax machines, all-in-ones, photo printers, and graphics plotters, to name a few.
Conventionally, a thermal inkjet printhead includes access to a local or remote supply of color or mono ink, a heater chip, a nozzle or orifice plate attached to or integrated with the heater chip, and an input/output connector, such as a tape automated bond (TAB) circuit, for electrically connecting the heater chip to the printer during use. The heater chip, in turn, typically includes a plurality of thin film resistors or heaters fabricated by deposition, patterning and etching on a substrate such as silicon. One or more ink vias cut or etched through a thickness of the silicon serve to fluidly connect the supply of ink to the individual heaters.
Heretofore, conventional heater chip thin films included a relatively thick silicon nitride (SiN) and silicon carbide (SiC) overlying a resistor layer for reasons relating to passivation. In turn, a cavitation layer overlies the two passivation layers to protect the heater from corrosive ink and bubble collapse occurring in the ink chamber. However, as layers continue to become thinner and more energy efficient over time, thinner passivation seems unable to provide adequate ESD protection. It some instances, the passivation is so thin that ESD events damage the resistor layer making it altogether inoperable.
Accordingly, the inkjet printhead arts desire ESD protection despite a continuing trend toward thinner heater chip configurations.